2015年10月26日星期一

Converted Sorted Array to Binary Search Tree


Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
http://blog.csdn.net/linhuanmars/article/details/23904883

Time: O(n)
Space: O(n)+O(logn)

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) { 
        return helper(nums, 0, nums.size() - 1);
    }
    TreeNode* helper(vector<int>& nums, int left, int right){
        if(left > right) return NULL;
        int mid = (left + right) / 2;
        TreeNode* root = new TreeNode(nums[mid]);
        root->left = helper(nums, left, mid - 1);
        root->right = helper(nums, mid + 1, right);
        return root;
    }
};
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